U.S. Pat. No. 5,025,974 describes a method of explosive bonding aluminium components together prior to superplastic forming and describes a method of heat treating the bonded components.
In explosive bonding, it is usual to place the components being bonded upon a substantial structure (known as an "anvil") and to place a plate (known as a "driver plate") on top of the components. Explosive is placed on top of the driver plate and detonated, the driver plate transmits the force of the explosion to the components, which are bonded together by such forces. By using a driver plate, damage to the surface of the topmost component is minimized. Using such a process it is possible to bond two or more components together.
One problem with the above process is that a bond can also form between the anvil and the composite bonded structure and/or between the driver plate and the composite structure and this makes removal of the structure from the anvil/driver plate difficult. To avoid this problem, common salt has been placed between the anvil and the components and between the components and the driver plate. Unfortunately, the force of the explosion causes air burning in the spaces between the components and the anvil/driver plate which degrades the components. Furthermore, the force generated by the explosion can cause the surfaces of the structure to become degraded as a result of their being forced against the anvil and driver plate.
In an effort to overcome these problems, it has been proposed to place sheets of rubber between the anvil and the components and between the components and the driver plate but unfortunately this does not completely eliminate the problem of air burning.
It has been proposed in EP-0 445 997 to protect a stack of sheets from damage during the explosive bonding step of an explosive bonding/superplastic forming process by coating the top and bottom surfaces of the stack with a resilient material and conducting the explosive bonding on a bed of common salt.